轴向磁场中电弧螺旋不稳定性的简化数值分析

在静电近似下，通过数量级的分析，简化了能量方程。用数值方法研究了外加轴向磁场，电流分布、弧电流等对电弧曙旋不稳定性的影响。数值结果表明，在具有外加磁场情况下，当弧柱内均匀电流分布时，正向磁场能够使短波长的扰动稳定，反向磁场能够使长波长的扰动稳定。当弧柱内电流为抛物线形分布时，外加正向磁场对于短波情况下的稳定性影响很小，但对于长波情况，稳定性增强，外加反向磁场，同样能稳定中等和长波情况下的电弧。     

磁驱动旋转电弧运动图像及弧电压脉动的实验研究

磁驱动旋转电弧产生扩散电弧等离子体过程中有许多有趣的物理现象。本文利用高速摄影技术研究了大气压条件下、非均匀磁场中、大尺度磁驱动旋转氩电弧的电弧结构；在一定的弧电流和外磁场条件下，电弧的平面形状表现为不断发展和增长的螺旋结构，电弧螺旋结构的破裂往往产生于阴极附近的等离子体射流。采用图像分析的方法计算了外部磁场作用下阳极斑点沿弧室内壁的移动频率，分析了磁驱动旋转电弧运动过程中的弧电压脉动现象。结合电弧图像分析和电弧电压脉动及其FFT分析得出：电弧电压的大幅波动与多层电弧螺旋结构破裂和重建相关，而电弧电压的小幅波动则是弧根小幅跳动引起电弧拉长和收缩的结果。     

Discussion on the Non-Equilibrium Phase of the Gliding Arc Plasma Driven by the Transverse Magnetic Field

a gliding arc driven by the transverse magnetic field was ignited between the electrodes with a complicated shape at atmospheric pressure and a non-equilibrium plasma was gencrated. Under our experimental conditions, a phenomenon was clearly observed where the arc power decreased with the increase in arc voltage. As the arc voltage was higher than 3.375 kV, the are power acquired from the power supply decreased, and the arc plasma began to switch to a non-equilibrium phase. The existence of the non-equilibrium arc plasma was very short, about 10 ms in one gliding arc discharge cycle.     

Parametric Study on Arc Behavior of Magnetically Diffused Arc

A model coupling the plasma with a cathode body is applied in the simulation of the diffuse state of a magnetically rotating arc.Four parametric studies are performed:on the external axial magnetic field (AMF),on the cathode shape,on the total current and on the inlet gas velocity.The numerical results show that:the cathode attachment focuses in the center of the cathode tip with zero AMF and gradually shifts off the axis with the increase of AMF;a larger cathode conical angle corresponds to a cathode arc attachment farther away off axis;the maximum values of plasma temperature increase with the total current;the plasma column in front of the cathode tip expands more severely in the axial direction,with a higher inlet speed;the cathode arc attachment shrinks towards the tip as the inlet speed increases.The various results are supposed to be explained by the joint effect of coupled cathode surface heating and plasma rotating flow.     

Study of Distortion of a Vacuum Arc at a Long-Gap Distance

Experimental study of the long-gap distance vacuum arc distortion for three types of axial magnetic field (AMF) contacts, by using high-speed charge coupled device (CCD), is presented. The arc current was of a half-cycle sine wave with a frequency of 50Hz, produced by an L-C discharging circuit. The time of appearance and duration of vacuum arc distortion under three conditions were studied. It was found that the gap distance, current and diameter of the electrode affected the characteristics of vacuum distortion at a long-gap distance. Some characteristics of the vacuum arc at a long-gap distance was revealed and the experience and data for further investigation were provided.     

Simulation Research of Magnetic Constriction Effect and Controlling by Axial Magnetic Field of Vacuum Arc

Based on magnetohydrodynamic (MHD) model of vacuum arc, the computer simulation of vacuum arc was carried out in this paper. In the MHD model, mass conservation equation, momentum conservation equations, energy conservation equations, generalized ohm‘s law and Maxwell equation were considered. MHD equations were calculated by numerical method, and the distribution of vacuum arc plasma parameters and current density were obtained. Simulation results showed that the magnetic constriction effect of vacuum arc is primarily caused by the Hall effect. In addition, the inhibition of axial magnetic field (AMF) on constriction of vacuum arc was calculated and analyzed.     

Arc Behaviours in Vacuum Interrupters with Axial Magnetic Field Electrodes

To improve the limiting current interruption capability and minimizing vacuum interrupter with axial magnetic field （AMF） electrodes, it is significant to investigate the vacuum arc behaviours between the contacts. AMF distributions of the slot type electrodes were studied by both numerical analysis and experiments. Furthermore, the behaviours of vacuum arcs for different parameters of the slot type AMF electrodes were investigated by using high-speed CCD camera. The influences of gap distance, contact diameter and phase shift time between AMF and arc current on the vacuum arc were investigated. The results provide a reference for research and development of vacuum interrupters with slot type or other types of AMF electrode.     

Characteristics of Single Cathode Cascaded Bias Voltage Arc Plasma

A single cathode with a cascaded bias voltage arc plasma source has been developed with a new quartz cathode chamber,instead of the previous copper chambers,to provide better diagnostic observation and access to the plasma optical emission.The cathode chamber cooling scheme is also modified to be naturally cooled only by light emission without cooling water to improve the optical thin performance in the optical path.A single-parameter physical model has been developed to describe the power dissipated in the cascaded bias voltage arc discharge argon plasmas,which have been investigated by utilizing optical emission spectroscopy(OES) and Langmuir probe.In the experiments,discharge currents from 50 A to 100 A,argon flow rates from 800 sccm to 2000 sccm and magnetic fields of 0.1 T and 0.2 T were chosen.The results show:(a) the relationship between the averaged resistivity and the averaged current density exhibits an empirical scaling law as η∝ j~(-0.63369) and the power dissipated in the arc has a strong relation with the filling factor;(b) through the quartz,the argon ions optical emission lines have been easily observed and are dominating with wavelengths between 340 nm and 520 nm,which are the emissions of Ar~+-434.81 nm and Ar~+-442.60 nm line,and theintensities are increasing with the arc current and decreasing with the inlet argon flow rate;and(c) the electron density and temperature can reach 2.0 × 10~(19) m~(-3) and 0.48 eV,respectively,under the conditions of an arc current of 90 A and a magnetic field of 0.2 T.The half-width of the n_e radial profile is approximatively equal to a few Larmor radii of electrons and can be regarded as the diameter of the plasma jet in the experiments.     

Simulation of Low-Voltage Arc Plasma During Contact Opening Progress

This paper focuses on the simulation of the low-voltage arc with an opening contact. A controllable experiment setup with a rotating contact is designed to investigate the arc behaviour. Supported by the experiment, the phenomena of arc elongation and commutation in the case of rotating contact are simulated with the dynamic grid technique introduced. Under the given condition of the external magnetic field and the contact rotating velocity, the stagnation and rapid jump of two arc roots are observed by the calculated and experimental arc root displacement. The voltage of arc column can be divided into four phases and its sharp rising progress comes from the increase of the displacement difference between two arc roots in x direction.     

Numerical simulation of low-current vacuumarc jet considering anode evaporation in different axial magnetic fields

As the main source of the vacuum arc plasma, cathode spots (CSs) play an important role on the behaviors of the vacuum arc. Their characteristics are affected by many factors, especially by the magnetic field. In this paper, the characteristics of the plasma jet from a single CS in vacuum arc under external axial magnetic field (AMF) are studied. A multi-species magneto-hydro-dynamic (MHD) model is established to describe the vacuum arc. The anode temperature is calculated by the anode activity model based on the energy flux obtained from the MHD model. The simulation results indicate that the external AMF has a significant effect on the characteristic of the plasma jet. When the external AMF is high enough, a bright spot appears on the anode surface. This is because with a higher AMF, the contraction of the diffused arc becomes more obvious, leading to a higher energy flux to the anode and thus a higher anode temperature. Then more secondary plasma can be generated near the anode, and the brightness of the ‘anode spot’ increases. During this process, the arc appearance gradually changes from a cone to a dumbbell shape. In this condition, the arc is in the diffuse mode. The appearance of the plasma jet calculated in the model is consistent with the experimental results.     

Simulation of arcs for DC relay considering different impacts

Recently DC relay has been concerned as a key component in DC power distribution,management and control systems like aircraft,new energy vehicle,IT and communication industries.Ordinarily,magnetic force and contact moving speed have great influence on arc behaviours in the breaking process.This paper focuses on the numerical investigation of arc during the contact opening process in a real 400V/20 A DC relay product coupling with an inductive load circuit.A 3D air arc model based on the magneto-hydrodynamic theory was built and calculated.A method coupling different computational software was used to take the nonlinear permanent magnet and contact opening process into consideration simultaneously.Arc behaviours under different magnetic field and contact opening speed were presented and discussed carefully.It has been found that the increase of the magnetic field is beneficial to the quick build-up of arc length and voltage.Arc breaking duration becomes shorter with the increase in contact opening speed from 63.5 rad s^-1 to 94.5 rad s^-1,such reduction is less significant with an increase of opening speed from 94.5 rad s^-l to 118.5 rad s^-1.     

Numerical simulation of the plasma acceleration process in a magnetically enhanced micro-cathode vacuum arc thruster

A particle-in-cell simulation is conducted to investigate the plasma acceleration process in a micro-cathode vacuum arc thruster. A coaxial electrode structure thruster with an applied magnetic field configuration is used to investigate the effects of the distribution of the magnetic field on the acceleration process and the mechanism of electrons and ions. The modeling results show that due to the small Larmor radius of electrons, they are magnetized and bound by the magnetic field lines to form a narrow electron channel. Heavy ions with a large Larmor radius take a long time to keep up with the electron movement. The presence of a magnetic field strengthens the charge separation phenomenon. The electric field caused by the charge separation is mainly responsible for the ion acceleration downstream of the computation. The impact of variations in the distribution of the magnetic field on the acceleration of the plasma is also investigated in this study, and it is found that the position of the magnetic coil relative to the thruster exit has an important impact on the acceleration of ions. In order to increase the axial velocity of heavy ions, the design should be considered to reduce the confinement of the magnetic field on the electrons in the downstream divergent part of the applied magnetic field.     

Numerical Simulation of Fluid Flow and Heat Transfer in a DC Non-Transferred Arc Plasma Torch Operating Under Laminar and Turbulent Conditions

In this work, a magnetic fluid dynamics (MHD) model is used to simulate the electromagnetic field, heat transfer and fluid flow in a DC non-transferred arc plasma torch under laminar and turbulent conditions. The electric current density, temperature and velocity distributions in the torch are obtained through the coupled iterative calculation about the electromagnetic equations described in a magnetic vector potential format and the modified fluid dynamics equations. The fluid-solid coupled calculation method is applied to guarantee the continuity of the electric current and heat transfer at the interface between the electrodes and fluid. The predicted location of the anodic arc root attachment and the arc voltage of the torch are consistent with corresponding experimental results. Through a specific analysis of the influence of mass flow rates and electric current on the torch outlet parameters, the total thermal efficiency, thermal loss of each part, and the laws of the variation of outlet parameters with the variation of mass flow rates and electric current was obtained. It is found that operation under a laminar condition with a limited area of the anode could increase the total thermal efficiency of the torch.     

Motion and Splitting of Vacuum Arc Column in Transverse Magnetic Field Contacts at Intermediate—Frequency

Arc motion and splitting of vacuum arc at intermediate frequency（400-800 Hz） were investigated under transverse magnetic field（TMF）.The experiment was performed on cup-type TMF contacts with contact diameter of 40 mm and a contact gap of 4 mm in a single-frequency circuit.With high-speed photography we characterized the arc appearance at different arc currents from 3.3 kA-rms to 10 kA-rms at intermediate frequencies.As arc current increases from3.3 kA-rms to 10 kA-rms the arc appearance changes obviously.When current value is 3.3 kArms（current frequency 400-800 Hz）,there is almost no splitting arc;when the current exceeds5 kA-rms（current frequency 400-800 Hz）,the arc rotates at a speed above 20 m/s,accompanied by an observable splitting arc.The splitting arc could be observed at different frequencies and the arc-voltage had no noises when splitting occurred.The motion direction and the velocity of arc column were studied.Finally,the formation of a split arc was discussed.     

Determination of the Velocity of a Magnetic-Field Driven Gliding Arc by Using a Photo-Multiplier

The gliding arc is an important approach to production of non-thermal plasma at atmospheric pressure, it can offer high-energy efficiency and high-electivity for chemical reactions. In this paper, the gliding arc driven by the transverse magnetic field is described and its velocity is measured by using a photo-multiplier. The mean velocity of the gliding arc increases with increasing magnetic induced-intensity, and its value varies from 7.8 m/s to 32 m/s.     

Study of double-chamber air arc plasma torch and the application in solid-waste disposal

Arc plasma can be applied in hazardous solid waste disposal for higher temperature than common heating methods, but some practical issues exist in practical engineering application. In this study, an air arc plasma torch with double chambers and magnetic controlling is designed to realize wide variable power and long electrode life. The detailed characteristics and laws of the air arc are studied. The condition parameters of arc current(I), air flow rate(G) and the structure parameters of inlet area ratios and electrode diameters influence both the arc voltage and arc root positions. The arc rotating driven by magnetic field effectively lengthens the electrode life. The gasification process and product of organic wastes by air plasma are influenced largely by the waste compositions and the air flow rate. A furnace structure with more even atmosphere and longer residence time should be considered for better gasification. Oxygen-deficient environment is important to suppress NOxformation during the application of air plasma. Inorganic solid wastes can be melt by the air plasma and cooled down to form compact vitreous structures in which heavy metals can be locked and the leaching rates significantly decrease down.     

Dynamic behavior of a rotating gliding arc plasma in nitrogen: effects of gas flow rate and operating current

The effects of feed gas flow rate and operating current on the electrical characteristics and dynamic behavior of a rotating gliding arc (RGA) plasma codriven by a magnetic field and tangential flow were investigated.The operating current has been shown to significantly affect the time-resolved voltage waveforms of the discharge,particularly at flow rate =21 min-1.When the current was lower than 140 mA,sinusoidal waveforms with regular variation periods of 13.5-17.0 ms can be observed (flow rate =21 min-1).The restrike mode characterized by serial sudden drops of voltage appeared under all studied conditions.Increasing the flow rate from 8 to 121 min-1 (at the same current) led to a shift of arc rotation mode which would then result in a significant drop of discharge voltage (around 120-200 V).For a given flow rate,the reduction of current resulted in a nearly linear increase of voltage.     

Comparative Observation of Ar, Ar-H2 and Ar-N2 DC Arc Plasma Jets and Their Arc Root Behaviour at Reduced Pressure

Results observed experimentally are presented, about the DC arc plasma jets and their arc-root behaviour generated at reduced gas pressure without or with an applied magnetic field. Pure argon, argon-hydrogen or argon-nitrogen mixture was used as the plasma-forming gas. A specially designed copper mirror was used for a better observation of the arc-root behaviour on the anode surface of the DC non-transferred arc plasma torch. It was found that in the cases without an applied magnetic field, the laminar plasma jets were stable and approximately axisymmetrical. The arc-root attachment on the anode surface was completely diffusive when argon was used as the plasma-forming gas, while the arc-root attachment often became constrictive when hydrogen or nitrogen was added into the argon. As an external magnetic field was applied, the arc root tended to rotate along the anode surface of the non-transferred arc plasma torch.     

Study on volt-ampere characteristics of solar array arcs in LEO spacecraft

The primary and secondary arcs volt-ampere characteristics of low earth orbit solar arrays are studied in this research. Using three gallium-arsenide solar cell samples, the gap lengths of the solar cell are set to 1, 2, and 3 mm. First, the primary arc voltage characteristics of a solar array are analyzed. It is found that two steps are involved in the primary arc voltages, which are 116 and 22 V according to our experiment and are independent of the electrostatic discharge current and the gap lengths. By comparing with the arc pattern, we determined that current chopping may be the reason for the stepped arc voltage. Then, the characteristics of the secondary arc of the solar array are demonstrated. The study shows that the secondary arc voltage values increase with the gap length. In the case of the same cell with a fixed gap length, the voltage of the secondary arc increases with the string current. Finally, the relationship between the secondary arc voltage and the gap length is obtained which helps the string voltage and the gap length selection for system design.     

Simulation of Vacuum Arc Characteristics Under Four Kinds of Axial Magnetic Fields and Comparison with Experimental Results

Based on a two-dimensional axisymmetric magnetohydrodynamic （MHD） model, the vacuum arc characteristics under four kinds of axial magnetic fields （AMFs） are ana...